Objectives Adolescents with type 1 diabetes (T1D) have shown improvements in glycemic control and family relations, via clinic-based family interventions. However, reach and clinician availability may be limited. We evaluated a self-directed intervention for this purpose. Methods Recruitment for a randomized controlled trial (RCT) occurred through national advertising with diabetes charities and conducted with online data collection. Parents of 11–17-year-olds with diabetes were randomized to usual care (n = 37) or intervention (n = 42) using computerized block randomization. The 10-week intervention comprised the Self-directed Teen Triple P workbook (10 × 1 hr modules) plus chronic illness tip sheet. Primary outcomes of diabetes-related family conflict and parenting stress were assessed pre and post-intervention. Results Intention-to-treat analyses (n = 79) identified significantly improved diabetes-related conflict, but not parental stress, compared with usual care. Conclusions The preliminary findings suggest that this could be a useful way to expand intervention reach for this population.